Acrylic acid is generally produced by subjecting propylene or acrolein to gas-phase catalytic oxidation in the presence of a catalyst to obtain an acrylic acid-containing gas, absorbing the acrylic acid-containing gas with an absorbing liquid or condensing the acrylic acid-containing gas to obtain an acrylic acid aqueous solution, and purifying acrylic acid with distillation or crystallization.
In an acrylic acid production process, a residue obtained by purifying acrylic acid contains a large amount of an impurity but also contains acrylic acid; therefore, acrylic acid is recovered from such a residue by distillation or the like. In addition, the above residue also contains acrylic acid dimer. Acrylic acid dimer is decomposed into acrylic acid to be recovered by heat using a heat decomposition apparatus consisting of a heat decomposition apparatus and an evaporator (Patent Document 1).
A residue after purifying acrylic acid by distillation has high viscosity, since such a residue contains a high-boiling impurity, a polymer and the like. When such a residue after distillation, in other words, a bottom liquid of a distillation apparatus, is discarded, it may be difficult to discharge and transfer the residue from the bottom of the distillation apparatus and the residue may not be stably stored in a storage tank in some cases. Such a problem would further become obvious in a distillation apparatus at latter stage of multistage distillation of acrylic acid and in a step of decomposing acrylic acid dimer by heat.
By the invention described in Patent Document 2, a handling property of waste oil generated from the production process of acrylic acid is improved by adding a solvent selected from water, an alcohol, an ether, a carboxylic acid, a ketone, an aliphatic hydrocarbon or an aromatic hydrocarbon to the waste oil. Patent Document 3 discloses a method for stabilizing a residue liquid remaining on a still after distilling a 2-hydroxyalkyl (meth)acrylate by adding water, acetic acid, salicylic acid, ethanolamines or methanol to the residue liquid.
It is described in Patent Document 4 that a high-boiling residue which remains in a reactor to decompose an acrylic acid oligomer is diluted with an organic acid, such as ethylhexanoic acid and propionic acid, or a hydrophilic organic liquid such as an alkanol, for example, ethanol and methanol in order to be incinerated.